Structural and chemical properties of zwitterionic iridium complexes featuring the tripodal phosphine ligand [PhB(CH2PPh2)3]-

Several new iridium compounds bearing the PhB(CH2PPh2)(3)(-) (herein abbreviated as [PhBP3]) ligand have been prepared and characterized, and a comparison of steric, electronic, and chemical properties is made with those of related pentamethylcyclopentadienyl (Cp*) and hydridotris(3,5-dimethylpyrazolyl)borate (Tp(Me2)) complexes. The complexes [PhBP3]Ir(H)(eta(3)-C8H13) (2) and [PhBP3]Ir(H)(eta(3)-C3H5) (3) were synthesized from the reaction of [Li-(TMED)] [PhBP3] (1) with the corresponding [(alkene)(2)IrCl](2) complex. These allyl complexes serve as precursors to the dihalides [PhBP3]IrX2 (10, X = I; 12, X = Cl). In addition to these dihalides, the five-coordinate species [PhBP3]IrMe2 (16) and [ClB(CH2PPh2)(3)]IrCl2 (13) have been isolated. Addition of CO to 2 or 3 gave [PhBP3]Ir(CO)(2) (7), while reaction of H-2 with 2 yielded {[PhBP3]IrH2}(2) (8) in benzene and [PhBP3]Ir(COE)H-2 (9) in THF (where COE = cyclooctene). Complex 2 reacted with PMePh2 to give [PhBP3]Ir(PMePh2)H-2 (5) and 1,3-cyclooctadiene. The protonation of 5 with [H(OEt2)]{B[3,5-C6H3(CF3)(2)](4)} gave the classical hydride complex {[PhBP3]Ir(PMePh2)H-3}{B[3,5-C6H3(CF3)(2)](4)} (6). In addition to the formation of allyl complexes 2 and 3, several C-H activation reactions have been observed; addition of PMe3 to 2 provided the cyclometalated product {PhB[(CH2PPh2)(2)(CH2PPhC6H4)]}Ir(H)(PMe3) (4) and COE. Photolysis of 5 gave {PhB[(CH2PPh2)(2)(CH2PPhC6H4)]}Ir(H)(PMePh2) (A) and [PhBP3]Ir(H)(PMePhC6H4) (B). Complex 9 catalyzes H/D exchange between COE and benzene-d(6). Metathesis reactions of diiodide 10 with LiBHEt3 gave [Li(THF)(n)]{[PhBP3]Ir(H)(2)I} (14a) and [Li(THF)(n)]{[PhBP3]Ir(H)(3)} (15). Comparison of the spectroscopic properties of related [PhBP3]Ir, Cp*Ir, and Tp(Me2)Ir complexes suggests that relative donating abilities follow the trend [PhBP3] greater than or equal to Cp* > Tp(Me2), and structural comparisons indicate that [PhBP3] is the most sterically demanding ligand.